Join Date: Feb 2010
Location: Narragansett Bay
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The first stage is the part attached to the tank that reduces the pressure down from 1000s of psi to something around 100 psi. You would never breath from a 100psi flow and the tank empties in less than a minute. The second stage, in a modern single hose rig, goes in your mouth and further reduces this flow to ambient pressure, only allowing flow upon demand when the suction you create by inhaling pulls on a bladder.
The first stage typically has several ports to which you attach your primary second stage regulator, your octupus (or backup second stage) and a pressure gauge that is directly ported to the tank without restriction.
Personally, I would prefer to clean the boat with a BC jacket on, so I could create positive bouyancy and put some pressure against the hull. Otherwise, each time to press to rub, you only manage to push yourself away. If you have a BC, you might as well carry the tank.
Sounds like you understand the basic principals of diving. It would be all but impossible to carry enought air to remain long enough to saturate nitrogen in less than 10ft of water, so dive table calcs are academic. However, air compression is still meaningful and if you exert yourself while rubbing, hold your breath and ascend accidentally, you could rupture alveoli in your lungs. Just be careful and always exhale!